1. Field of the Invention
The present invention relates to an electron emitting apparatus.
2. Related Background Art
Up to now, as the electron emitting device, there have been roughly known two kinds of electron emitting devices consisting of a thermionic cathode and a cold cathode. The cold cathode are of the field emission type (hereinafter referred to as xe2x80x9cFE typexe2x80x9d), the metal/insulating layer/metal type (hereinafter referred to as xe2x80x9cMIM typexe2x80x9d), the surface conduction type electron-emitting device, and so on.
The examples of the FE type electron emitting devices have been known from xe2x80x9cField emissionxe2x80x9d of Advance in Electron Physics, 8,89 (1956) by W. P. Dyke and W. W. Dolan, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d of J. Appl. Phys., 47,5248 (1976) by C. A. Spindt, U.S. Pat. No. 5,864,147, and so on.
The examples of the MIM type electron emitting devices have been known by xe2x80x9cOperation of tunnel-emission devicesxe2x80x9d of J. Apply. Phys., 32,646 (1961) by C. A. Mead, and so on.
Also, the recent examples have been introduced by xe2x80x9cFluctuation-free electron emission from non-formed metal-insulator-metal (MIM) cathodes fabricated by low current anodic oxidationxe2x80x9d of Jpn. J. Appl. Phys. vol. 32 (1993) pp. L1695, by Toshiaki Kusunoki, xe2x80x9cAn MIM-cathode array for cathode luminescent displaysxe2x80x9d of IDW xe2x80x296 (1996) pp. 529 by Mutsumi Suzuki, et al, and so on.
The examples of the surface conduction type electron-emitting devices have been disclosed in EP-A-0660357, EP-A-0701265, xe2x80x9cElectron trajectory analysis of surface conduction type electron emitter displays (SEDs)xe2x80x9d of SID 98 DIGEST, pp. 185-188 by Okuda et al, EP-A-0716439, and so on. The surface conduction type electron-emitting devices are so designed as to utilize a phenomenon in which electrons are emitted by allowing a current to flow into a small-area thin film formed on a substrate in parallel with the film surface.
The above-mentioned surface conduction type electron emitting devices are of the planar type schematically shown in a plan view of FIG. 18A and a cross-sectional view of FIG. 18B, and of the vertical type schematically shown in cross-sectional views of FIGS. 19A and 19B. In FIGS. 18A, 18B, 19A and 19B, reference numeral 181 denotes a substrate, 182 and 184 are electrodes, 186 is an electroconductive film, 185 is a gap and 193 is a step forming member.
FIGS. 20 and 21 schematically show appearances in which the devices shown in FIGS. 18A, 18B, 19A and 19B are driven, respectively. In FIGS. 20 and 21, the same members as those in FIGS. 18A, 18B, 19A and 19B are designed by identical references.
In the conventional surface conduction type electron emitting device, electrons are tunneled from the electroconductive film 186 connected to the electrode 182 which is at a lower potential side to the electroconductive film 186 connected to the electrode 184 which is at a higher potential side. Then, the electrons thus tunneled reach an anode electrode 203 after the electrons are scattered on the higher-potential side electrode 184 and/or the higher-potential side electroconductive film 186 plural number of times. Parts of the tunneled electrons are taken into the higher-potential side electrode or the electroconductive film during the above scattering process, as a result of which sufficient electron emission efficiency cannot be ensured. In the present specification, the electron emitting efficiency is directed to a ratio of an emission current (Ie) that reaches the anode electrode 203 to a device current (If) that flows between the electrode 182 and the electrode 184 when the above device is driven.
In order to realize the image display device, electrons emitted from the electron emitting device are allowed to collide with the anode electrode having a phosphor to emit a light. However, in the image display device that requires a higher-precision image, it is necessary that the electron trajectories are converged, the electron emitting device is downsized, and the electron emission efficiency is improved. In general, as the characteristic of the electron emitting device, the electron emission efficient and the convergence of the electron trajectories have a relationship of trade-off, and it is difficult to satisfy the above conditions together.
The present invention has been made to solve the above problems, and therefore an object of the present invention is to provide an electron emitting apparatus that can realize the convergence of electron trajectories and an improvement of the electron emission efficiency together.
In order to achieve the above object, according to the present invention, there is provided an electron emitting apparatus, comprising:
(A) a substrate having a first primary surface which is substantially plane;
(B) an electron emitting device disposed on the first primary surface, comprising a first electroconductive member and a second electroconductive member which are disposed at an interval;
(C) an anode electrode having a substantially plane surface opposite to the first primary surface;
(D) voltage applying means for applying a potential higher than a potential applied to the first electroconductive member to the second electroconductive member in order to emit electrons from the electron emitting device; and
(E) voltage applying means for applying a potential higher than the potential applied to the second electroconductive member in order to irradiate the electrons emitted from the electron emitting device onto the anode electrode;
wherein a through-hole (opening) that penetrates the second electroconductive member is defined in a part of the second electroconductive member which exists within a range from the gap to a distance Xs represented by the following expression (1), an electroconductive member to which a potential lower than said second electroconductive member is applied is disposed under said through-hole; and
Xs=Hxc3x97Vf/(xcfx80xc3x97Va)xe2x80x83xe2x80x83(1) 
where H is a distance between a plane of the anode electrode and the first primary surface, Vf is a voltage applied between the first electroconductive member and the second electroconductive member, Va is a voltage applied between the anode electrode and the first electroconductive member, and xcfx80 is the ratio of the circumference of a circle to its diameter.